The invention relates to a method of measuring a stress wave used in breaking rock, the method comprising measuring a stress wave which propagates in a waveguide.
The invention further relates to a measuring device for measuring a stress wave, the device comprising: at least one measuring member; and at least one control unit for processing measurement results.
The invention further relates to a rock breaking device which comprises: a frame; a tool; a device for generating stress waves in the tool; measuring means for measuring the stress wave travelling in the tool; at least one control unit for controlling the rock breaking device on the basis of the measured stress wave.
Rock breaking may be performed by drilling holes in a rock by a percussion rock drilling machine. Alternatively, rock may be broken by a breaking hammer. In this context, the term “rock” is to be understood broadly to also cover a boulder, rock material, crust and other relatively hard material. The rock drilling machine and breaking hammer comprise a percussion device, which gives impact pulses to the tool either directly or through a shank. In other words, the percussion device is used to generate a compression stress wave in the tool, where the wave propagates to the outmost end of the tool. When the compression stress wave reaches the tool's outmost end, the tool penetrates into the rock due to the influence of the wave. Some of the energy of the compression stress wave generated by the percussion device is reflected back as a reflected wave, which propagates in the opposite direction in the tool, i.e. towards the percussion device. Depending on the situation, the reflected wave may comprise only a compression stress wave or a tensile stress wave. However, the reflected wave typically comprises both the tension and the compression stress component. The stress wave travelling in the tool may be measured and the measurement result employed in controlling a rock breaking device as described in U.S. Pat. No. 4,671,366, for example. Typically, resistance strain gauges are used in measuring the stress wave but the attachment of the gauges poses a problem. It is difficult to glue strain gauges to the tool. U.S. Pat. Nos. 6,356,077 and 6,640,205 further describe arranging a coil around the tool for measuring magnetostrictive or magnetoelastic changes caused by stress waves in the tool. A problem associated with these inductive methods is that the consistence and magnetic history of the tool's material affect the measurement accuracy.